The present invention relates to an adaptive packet routing system in a packet network and more particularly to a routing system using a neural network in which respective nodes maintain a neural network and which determines an optimum output direction of a packet from the self node or source node by using the neural network.
A future communication network will require increased operation speed and capacity and is expected to develop into a multimedia integrated network in which various media can be installed in a mixed manner. In such an integrated network, the required performance such as a communication speed, reliability and a real time operation varies with time. Therefore, a routing technique is necessary which can set a flexible communication path in accordance with a variation of a state of a network and can set a detour path immediately upon an occurrence of a fault.
As a technology of realizing such communication, a packet exchange network has been considered. As an exchange method in a packet exchange network, a datagram method is provided which does not set a logical link between terminals, namely, which does not use a concept of a call, or a virtual call method which provides a logical channel between terminals. In a datagram system operated in such a packet exchange network, routing information up to the destination node is rewritten depending on the changes of the state of the network. This is because the traffic variation is relatively small and the optimum path is assumed not to frequently vary. In the routing of the virtual call method, the amount of traffic to be using a network is predicted upon designing the network and thus the optimum route is obtained so that the predicted traffic is not concentrated on a particular node between the sending and receiving node.
FIG. 1 shows a prior art example of the routing system in a packet exchange network. In FIG. 1, a packet is transmitted from a sending node (A) 1 to a receiving node (B) 2 and paths 1 to n exists between a sending node 1 and a receiving node 2. Routing tables for providing optimum path information are provided in respective nodes for each requested quality of the information such as the requested band of the media, and the path determination is made based on the content of these tables.
In the virtual call, a plurality of detour routes are provided between transmitting and receiving nodes so that a faulty portion can be avoided. When the fault occurs, a default path is provided between transmitting and receiving nodes, thereby re-opening communication in a virtual call.
FIG. 2 shows a prior art of establishing a fault detour route in a packet exchange network. In FIG. 2, between terminals A and B a route going through nodes 3, 4 and 5 are provided as an optimum route, and routes going through nodes 3, 6, 4 and 5 and going through nodes 3, 6, 7 and 5 are provided as a detour route. Between terminals C and D a route going through nodes 4, 6 and 8 are provided as an optimum route and a route going through nodes 4, 5, 7 and 8 are provided as a detour route.
As described above, in the prior art routing of a datagram method, it becomes necessary that a routing table from a source node to a destination node is periodically updated in accordance with the change of the state of the network as shown in FIG. 3. When the scale of the network becomes large and further the traffic variation is large, there is a problem that a time required for calculating an optimum path increases explosively and that an adaptive routing cannot be realized in accordance with the always changing state.
Even if an optimum path is obtained upon an input of the packet by using a virtual call system, a rate of a change of media kind & quantity installed therein with time becomes extremely large as compared with the prior art packet exchange network, it is impossible to obtain or determine an optimum path per the kind of media and the state of network by predicting such aspects of the network. In addition, there is a problem that a time for calculating an optimum path explosively increases with the scale of the network. There is also a problem that, if a detour path is again determined between a transmitting and receiving node when a link or node fault occurs, communication of a virtual call is interrupted during the period from the occurrence of the fault to the setting of the detour circuit, thereby reducing the reliability of a communication.
In the prior art, a single media is usually to be dealt with by a network and thus routing which satisfies different quality requests from various medias is not always carried out. In the multimedia integrated network it is necessary to realize a routing which satisfies a quality required by each of medias.
To realize such routing, we applied patent applications (Tokuganhei 01-507916 filed on Jul. 6, 1989 and U.S. application Ser. No. 455,323 filed on Jul. 6, 1989) in which a routing adaptive to a state of the network is realized by a control network interconnecting threshold elements.
In the above applications, a threshold element corresponding to a neuron is provided to each node, thereby forming a neural network in the whole actual network. In this case, a time required until the neural network becomes stable and the optimum path is obtained depends on the distance between the nodes and thus there is a problem that a network with a long distance between the nodes is not adaptive to the state variation.